A network domain can be considered to comprise any collection of network elements within a common sphere of address management or path computational responsibility.
Interoperability between different network domains is a key enabler for allowing new technologies to be introduced, and for enabling cost effective transport services to be provided. Interoperability reduces the cost of network deployment as equipment and technology becomes available from multiple sources. The cost of operating a network can be reduced since processes can be streamlined over multiple technologies and vendor equipment.
Interoperability can be addressed at different levels, for example at component level, sub-system and system level and among different network domains and layers, and finally at a data and control plane.
FIG. 1 shows a prior art network architecture whereby multiple network domains 101, 102, 103 are interconnected according to proposals established by the Optical Internetworking Forum (OIF) and the Internet Engineering Task Force (IETF). Network architectures such as those shown in FIG. 1 rely on interfaces known as External Network-to-Network Interfaces (E-NNI) 104, 105, 106 being provided between separate administrative domains (i.e. between network domains 101, 102, 103), thereby allowing client devices 107, 108, 109 to communicate.
The E-NNI is based on the advertisement of a chosen set of domain related information outside its boundaries towards the other administrative domains of the network so as to allow different path computation elements (PCEs) to compute end-to-end paths and related protection/restoration schemes spanning multiple network domains. According to existing standards, path computation over multiple network domains is performed either centrally or in a distributed manner. These are mutually exclusive schemes in the existing standards. Such a framework relies on specific signaling protocols. Standardization bodies are therefore defining a single signaling procedure spanning multiple domains. As such, a prerequisite for interoperability between different network domains according to the prior art is the provision of global standards and specifications.
A disadvantage of such a framework is that it prevents all of the various implementations provided by different network operators or vendors (in the different network domains) from using any customized features, since customized features would not be “understood” by nodes from different vendors.
Furthermore, since mature implementations based on these specifications have to interwork seamlessly, this means that all implementation options are eliminated or transformed to obligatory features. Only mandatory features are retained, and all interpretations of the standards are streamlined. These are further disadvantages of existing frameworks for interoperability between different network domains.